Garage conversion

I have to replace a garage roof (the existing roof is timber and roofing iron) and would like the new roof to use steel beams and batterns and new colourbond roofing. When I have done this before in timber I would look up the span tables and buy the appropriate materials. But I am keen to do steel as it is white ant proof. So my questions are.... Where can you get span tables for steel beams? What steel section is best to use to span 4 metres? and What are the fixing requirements needed...

More...